How did geographic conditions limit contact between africans and people from outside of the middle east?

Sahara desert was a large isolating buffer that prevents eastern and sub-saharan African peoples from consistent contact with other peoples. The middle east was the only civilzation with land connection to the rest of Africa an stood in between Africans and the rest of the known world.

from the conditions of the working class in england by friedrich engels,the main idea is :

the answer is jerusalem